This invention relates generally to printing bank checks or similar documents or object using different types of inks and more particularly to an electrostatic printing apparatus and developer therefor for forming toner images comprising characters suitable for recognition by character recognition devices and ones that are not recognizable by such devices. The different types of toner may be the same color or different colors. Also, they are preferably created using magnetic and non-magnetic toners.
The invention can be utilized in the art of xerography or in the printing arts. In the practice of xerography, it is the general procedure to form an electrostatic latent image on a xerographic surface by first uniformly charging a photoconductive insulating surface, photoreceptor or photoconductor. The charge is selectively dissipated in accordance with a pattern of activating radiation corresponding to original images. The selective dissipation of the charge leaves a latent charge pattern on the imaging surface corresponding to the areas not struck by radiation.
This charge pattern is made visible by developing it with toner. The toner is generally a colored powder which adheres to the charge pattern by electrostatic attraction.
The developed image is then fixed to the imaging surface or is transferred to a receiving substrate such as plain paper to which it is fixed.
This method of forming and developing charge patterns, in general is set forth in greater detail in U.S. Pat. No. 2,297,691 to C. F. Carlson. Still other means of forming and developing electrostatic images are set forth in U.S. Pat. No. 2,647,464 to J. P. Ebert; U.S. Pat. No. 2,576,047 to R. M. Schaffert and U.S. Pat. No. 2,825,814 to L. E. Walkup,
The use of different type of toner for electrostatically forming the images on a single substrate is disclosed in U.S. Pat. Nos. 4,572,647 issued on Feb. 25, 1986 to Bean et al and 4,509,850 issued on Apr. 9, 1985 to Weigl. The former patent discloses the use of charged insulating marking particles in combination with magnetic polar or polarizable marking particles while the latter discloses the use of polar or polarizable marking particles in combination with charged marking particles.
The use of a single developer composition for creating magnetically recognizable characters has been employed for creating bank checks as disclosed in U.S. Pat. No. 4,517,268 issued on May 14, 1985 to Gruber et al. As disclosed in this patent, the entire clock is printed using such developer.
In U.S. Pat. No. 4,128,202 is disclosed a device for transporting a document that has been mutilated or erroneously encoded wherein there is provided a predetermined area for the receipt of correctly encoded magnetic image character recognition information (MICR).
In contrast to the '202 patent where only a predetermined area of the substrate is encoded or printed with MICR information, the '268 patent discloses the printing of the entire check or substrate using developer materials which are compatible with MICR technology. Such toners have come to be known as MICR toners.
MICR toners are more expensive compared to standard black (i.e. non-magnetic) toners because of the required intrinsic quality of the magnetic ingredients. In addition, the magnetic characters must be positioned and aligned correctly on the check (or document) to enable the magnetic heads to read the characters without error. This places limits on how well the magnetic information bearing parts of the document must be registered with the other printed information. Another problem is that the only way MICR toner can be incorporated into a colored document now is to use a pre-printed form or to employ two-pass xerography or as in the '268 patent to print the entire check or document using the more expensive MICR developer. Each of these methods involve penalties; two of them in cost and the other in throughput.